In applications such as ship hulls or bridge decks, the steel plates forming such constructions are generally stiffened to increase stiffness and strength by preventing localised plate buckling. The stiffeners may be comprised of plates, cold formed or rolled sections that are welded orthogonally to the main load bearing plate. These are generally equally spaced and may be oriented in one or two directions that are aligned with the plan dimensions of the main plate. The number, size, location and type are dependent on the application and the forces that must be carried by the structure. The use of stiffeners requires welding, complicates the manufacturing process and adds weight. Stiffeners, their connection to the main plate or intersection with other main framing members are often the source of fatigue and corrosion problems. Complex and congested structures that result from combining stiffened plates are often difficult to maintain and to provide adequate corrosion protection.
Metal-foam laminates with improved sound or heat insulating properties ate known for use in cladding or roofing buildings, see for example U.S. Pat. No. 4,698,278. Such laminates generally employ foamed or fibrous materials and are not intended to, nor capable of, bearing significant loads, i.e. significantly greater than self-weight and small loads due to localised wind or snow action. Not withstanding, the use of a steel-polyurethane foam-steel sandwich was investigated for use in hulls in ships. It was concluded that this type of sandwich construction was unsuitable as it did not have sufficient bond strength to provide equivalent in-plane or transverse stiffness and strength to stiffened plate structures that is required to carry the applied loads.
GB-A-2 337 022 discloses the use of an intermediate layer comprised of an elastomer located between and adhered to the inner surfaces of first and second metal layers.